US 2008/0141768 discloses ice detection for a wind turbine, wherein a wind velocity is measured with an anemometer.
US 2005/0276696 discloses methods and an apparatus for rotor blade ice detection, wherein meteorological conditions are monitored and wherein a parameter that varies with the mass of a rotor blade or a mass imbalance between the rotor blades is monitored.
WO 02/053910 discloses a method and a device for monitoring the state of rotor blades on wind turbines, wherein a rotor blade immanent sensor is used to identify a damage on the rotor blade.
US 2008/0206052 discloses a method and a device for monitoring the state of rotor blades on wind power installations, wherein a displacement sensor is arranged on the rotor blade.
EP 1 959 134 discloses a method and a system for utilizing lateral tower acceleration to detect asymmetric icing, wherein a determination whether a rotor-mass imbalance exists is performed.
EP 1 936 186 discloses a wind turbine and a method of detecting asymmetric icing on a wind turbine, wherein it is determined, whether a rotor-mass imbalance condition exists utilizing longitudinal tower acceleration data. Hereby, a rotor speed acceleration monitoring system is utilized.
EP 1 748 185 discloses an icing detection system for a wind turbine, wherein a digital structural vibration sensor measures a vibrational condition or a load condition of the wind turbine and delivers the measurement data to a detection means which is adapted to detect an icing condition on the basis of the mechanical variable data provided by the structural vibration sensor.
There may be a need for a method and a system for determining a mass change, in particular an icing condition, at a rotating blade of a wind turbine which is capable of determining an icing condition in a more accurate manner and which is capable of determining the icing condition in a simplified way. In particular, there may be a need for a method and a system for determining a mass change, in particular an icing condition, at a rotating blade of a wind turbine, which can easily be used or installed or performed in an existing wind turbine without requiring major structural modifications or adaptations. Further, there may be a need for a method and a system for determining a mass change, in particular an icing condition, at a rotating blade of a wind turbine which is reliable and cost-effective.